HARD TO START WHEN WARM

MY 2002 GMC SIERRA 1500 Z71 4.8L 4 WH DR
STARTS GOOD WHEN COLD BUT IF IT SITS FOR MORE THAN FIVE MINUTES OFF, IT IS HARD TO START I HAVE TO CRANK IT QUITE A WHILE TO START IT. AFTER 5 0R SIX HOURS OFF IT WILL START RIGHT UP.
I TRIED SPRAYING THROTTLEBODY CLEANER IN IT BUT IT DID NOT HELP.